1. Field of the Invention
This invention relates generally to the wheel alignment art and more particularly relates to wheel clamps which engage a wheel rim to support a wheel alignment measuring device in a plane generally parallel to the plane of the wheel rim.
2. Description of the Prior Art
Wheel clamps of varying design have long been used to support wheel alignment measuring devices in a plane generally parallel to the plane of the wheel rim. Typically, the clamp will have three or four rim-engaging fingers adapted to grasp a peripheral lip extending around the wheel rim and projecting outward therefrom. An outwardly extending shaft is aligned with the center of the wheel and is attached to the wheel clamp for supporting the wheel alignment measuring device. Such a wheel clamp is disclosed in the U.S. Pat. No. 2,475,502, to Holmes issued on July 5, 1949.
The wheel alignment measuring device that is supported by the wheel clamp may be any of a variety of devices well-known in the field. The wheel clamp of the present invention is designed in particular to support a projector which is mounted on the front wheel of the vehicle to project a beam toward a second projector mounted by a second clamp on the opposite front wheel. Each projector has a plurality of light sources to project a plurality of beams, one at a time, in a diverging pattern. Each projector also has a detector to sense the presence of beams projected from the opposite projector. Circuitry is provided to identify the beam which is detected, at any angle of toe of the wheel, to thereby provide a reading for the angle of toe. Such a projector is described in U.S. Pat. No. 4,180,326 to Chang, issued on Dec. 25, 1979.
The wheel alignment measuring device of the aforedescribed patent includes a base which is journaled for free rotation on the clamp shaft so that the device remain in its pendulous position as the wheel (and clamp) is rotated. A gravity sensor included within the base detects the vertical deflection of the wheel as the wheel is rotated. A barrel extending forward of the base includes an array of light emitting diodes (LED's) for projecting beams used in detecting the toe of the front wheels. A detector head mounted at the forward end of the barrel includes a 45.degree. mirror for projecting the array of beams transversely with respect to the vehicle so that they may be detected by the second wheel alignment measuring devise mounted on the opposite vehicle wheel.
The operation of such a wheel alignment measuring system is well described in the patent to Chang, referenced hereinbefore, and in U.S. Pat. No. 4,150,897 to Roberts Jr, et al. To understand the present invention, it is necessary only to note that the barrel of the device must extend forward of the front of the tire and, in some cases, in front of the vehicle in order for the pair of projectors to communicate with one another. With prior wheel clamps, this has required that the barrel be long enough to extend from the center of the wheel past the front of the tire. With large vehicles, such as trucks, the distance between the center and the front of the wheel requires a barrel of excessive length. It becomes more difficult, and thus more expensive, to produce the larger projector required for use on trucks and other large vehicles.